Friday, August 17, 2012

The Science of a Vegetarian/Vegan Diet

Upon hearing that I am vegetarian or vegan, many people ask me, where do you get your protein from?  And other similar nutrition questions concerning my vitamin intake.  The following information is compiled from one of my nursing text books.  It's a bit lengthy but provides good information.  If you don't want to read it in its entirety, skip ahead to Protein Sources, Types of Vegetarians, or Vitamin and Mineral Sources.

From Williams' Basic Nutrition & Diet Therapy 12th Edition by Staci Nix (my text book for nursing school):

"Amino acids: nitrogen-bearing compounds that form the structural units of protein. When digested, the various food proteins yield their constituent amino acids, which are then available for use by the cells to synthesize specific tissue proteins (e.g. collagen in connective tissue, myosin in muscle tissue, hemoglobin in red blood cells, digestive enzymes or hormones). Protein is used for tissue building, energy system, water balance, metabolism, and body defense system (immune system).

Protein foods that contain all nine indispensable amino acids in sufficient quantity and ratio to meet the body's needs are called complete proteins. These proteins are primarily of animal origin (e.g. egg, milk, cheese, and meat.) However, soybeans and soy products are the exception. Soy products are the only plant sources of complete proteins.

Protein foods that are deficient in one or more of the nine indispensable amino acids are called incomplete proteins. These proteins generally are of plant origin (e.g. grains, legumes, nuts, seeds, vegetables, and fruits) but are found in foods that make valuable contributions to the total dietary protein.

Current knowledge of protein metabolism and the "pooling" of amino acid reserves, indicates that a mixture of plant proteins can provide adequate amounts of amino acids when the basic use of various grains is expanded to include soy protein and other dried legume proteins (i.e. beans and peas).

Because most plant proteins are incomplete, lacking one or more indispensable (or essential) amino acids, match plant foods so that the amino acids missing in one food are supplied in another. This is the art of combining plant protein foods so that they "complement" one another and supply all nine indispensable amino acids.

Normal eating pattern through the day, together with the body's reserve supply of protein, usually ensures a complementary amino acid balance. The underlying requirement for vegetarians, as for all people, is to eat a sufficient amount of varied foods to meet normal nutrient and energy needs.

The indispensable amino acids are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.  In making the needed amino acids, families of foods (e.g. grains, legumes, and dairy) must be mixed.  For example, grains are low in threonine and high in methionine, whereas legumes are just the opposite – low in methionine, and high in threonine.  Therefore grains and legumes help balance one another in the accumulation of all indispensable amino acids.  The addition of milk products and eggs enhance the amino acid adequacy for lacto-ovo-vegetarians.  Here are a few sample food combination dishes to illustrate complementary protein combinations:  (The book did not list specific food sources for each amino acid.)

1.    Grains and peas, beans and lentils:  brown rice and beans, whole grain bread with pea or lentil soup, wheat or corn tortilla with beans, peanut butter on bread, Indian dishes of rice and dal (a legume), Chinese dishes of tofu and rice

2.    Legumes and seeds:  falafel, soybeans and pumpkin or sesame seeds, Middle Eastern hummus (garbanzo beans and sesame seeds) or tahini

3.    Grains and dairy:  whole wheat pasta and cheese, yogurt and a multi-grain muffin, cereal and milk, cheese sandwich with whole grain bread


Vegetarian diets differ according to the beliefs or needs of individuals following these food patterns. Approximately 2.5% of the total U.S. population followed a vegetarian diet in 2000. There are a variety of reasons that lead people to choose a vegetarian diet: environmental or animal cruelty concerns, health reasons, religions adherence (e.g. Buddhism, Hinduism, Seventh Day Adventists, and Zen), or aversion to consuming animal products. A diet void of animal products is not always a choice. In some areas in the world, vegetarianism is simply a result of the lack of resources and availability of animal products.

 In general there are four basic types:

1. Lacto-ovo-vegetarian: follow a food pattern that allows dairy products and eggs. Their mixed diet of plant and animal food sources, excluding only meat and fish, poses no nutritional problems.

2. Lacto-vegetarian: accept only dairy products from animal sources to complement their basic diet of plant foods. The use of milk and milk products (e.g. cheese) with a varied mixed diet of whole or enriched grains, legumes, nuts, seeds, fruits, and vegetables in sufficient quantities to meet energy needs provides a balanced intake.

3. Ovo-vegetarian: The only animal foods included in the ovo-vegetarian diet are eggs. Because eggs are an excellent source of complete proteins, individuals following this diet do not have to be overly concerned with complementary proteins on a daily basis.

4. Vegans: follow a strict vegetarian diet and use no animal foods. Their food pattern is composed entirely of plant foods (e.g. whole or enriched grains, legumes, nuts, seeds, fruits, and vegetables).  The use of soybeans, soy milk, soybean curd (tofu), and processed soy protein products enhances the nutritional value of the diet, and these products are well-tolerated and accepted. Careful planning and sufficient food intake ensure adequate nutrition.

The American Dietetic Association's current position paper on vegetarian diets indicates that the former conscious combining of complementary plant proteins within every given meal is unnecessary. It is more important to achieve balance throughout the day.


There have been many debates about the adequacy of vegetarian diets. Studies have found individuals following a vegan diet to have an inadequate intake of various nutrients, including protein, calcium, phosphorus, zinc, selenium, vitamin D, vitamin B12 (cobalamin), and riboflavin (B2). Additional concerns are warranted in studies that find reduced albumin synthesis, an important endogenous protein, and reduced iron stores in men and women following vegetarian diets. Following is a list of food sources: (I left meat options off of the Significant Fool Sources.)

1.    Calcium: primary sources are milk; milk products (yogurt, cheese, ice cream); calcium-fortified tofu; fruit juices; other food products (e.g. cereals, bars, etc.); low-oxalate greens such as bok choy, broccoli, collards, kale and turnip; oxalic acid in spinach, rhubarb, Swiss chard, and beet greens. Secondary sources are grains, legumes, and nuts. (Significant Food Sources of Calcium: Bran muffin, whole wheat bread, corn muffin, Cream of Wheat cereal, enriched pasta, enriched rice, Wheat Flakes cereal, artichoke, asparagus, raw avocado, raw broccoli, Brussels sprouts, carrots, collards, kale, green peas, potato with skin, raw apricots, figs, orange juice, raw navel orange, raw papaya, raw raspberries, raw strawberries, raw tangerine; almonds, cashews, egg, kidney beans, lentils, lima beans, peanuts, soybeans, tofu; yogurt, milk, Barbados molasses, brown sugar.)

2.    Phosphorus: found in all animal and plant cells; primary sources are milk, milk products, meat, fish, eggs; secondary sources are cereal grains, beans, peas, other legumes, nuts. (Significant Food Sources of Phosphorus: bran flakes, bran muffin, whole wheat bread, English muffin, oatmeal, enriched pasta, enriched rice, wheat flakes cereal, artichoke, raw avocado, Brussels sprouts, yellow corn, green peas, potatoes with skin, spinach, sweet potato; figs, orange juice, seedless raisins; almonds, black-eyed peas, chickpeas (garbanzo beans), cod, egg, halibut, lentils, peanut butter, peanuts, pinto beans, sole, soybeans, tofu, rainbow trout, tuna, walnuts; cheddar cheese, cottage cheese, milk, Swiss cheese, yogurt.)

3.    Iron: Primary sources are meat, eggs, vegetables, and cereals. (Significant Food Sources of Iron: bran flakes cereal, bran muffin, whole wheat bread, Cream of Wheat, oatmeal, pasta, rice, wheat flakes, artichoke, raw avocado, broccoli, Brussels sprouts, green peas, potato with skin, spinach, dates, figs, prune juice, prunes, raisins, almonds, black-eyed peas, cashews, chickpeas, egg, halibut, lentils, lima beans, mackerel, pinto beans, sole, soybeans, tofu, rainbow trout, tuna, black molasses, brown sugar.) FYI: the body absorbs iron more easily when taken with vitamin C.

4.    Zinc: primary sources are meat, seafood (esp. oysters). Secondary sources are legumes and whole grains. (Significant Food Sources of Zinc: bran muffin, whole wheat bread, Cream of Wheat, English muffin, oatmeal, pasta, wheat flakes, artichoke, asparagus, raw avocado, Brussels sprouts, collards, green peas, potato with skin, raw apricots, raw cantaloupe, figs, almonds, cashews, chickpeas, egg, kidney beans, lentils, lima beans, peanuts, soybeans, tofu, milk, yogurt.)

5.    Selenium:  primary sources are seafood, kidney and liver.  Secondary sources are other meats.  More variable are grains and other seeds depending on the selenium content of the soil in which they are grown.  Fruits and vegetables generally contain little selenium.

6.    Riboflavin (B2):  primary source is milk. Secondary sources are enriched grains and animal protein, sources, such as meats (esp. beef liver), poultry, and fish.  Vegetables such as mushrooms, spinach, and avocados are good natural sources.  (Significant Food Sources:  bran flakes, English muffin, enriched noodles, enriched spaghetti, wheat flakes cereal, asparagus, raw avocado, mushrooms, spinach, sweet potato, figs, prunes, raw raspberries, almonds, egg, kidney beans, lentils, lima beans, mackerel, rainbow trout, soybeans, brie cheese, buttermilk, cheddar cheese, cottage cheese, milk, ricotta cheese, yogurt.

7.    B12 (cobalamin):  primary sources are beef, chicken liver, lean meat, clams, oysters, herring, and crab.  (Significant Food Sources:   Total Wheat Cereal, egg, herring, mackerel, mussels, oysters, salmon, swordfish, tuna, cheddar cheese, milk, Swiss cheese, yogurt.)

8.    Vitamin D:  only yeast and fish liver oils are natural sources.  Regular food sources are fortified with Vitamin D.  (Significant Food Sources:  corn flake cereal, granola, raisin and bran cereal, egg, evaporated milk, milk, margarine, fish oil.)  Also, from sunlight.  "The amount needed may vary between winter and summer, and with individual exposure to sunlight."  People regularly exposed to sunlight (e.g. under appropriate conditions have no dietary requirement for vitamin D.  A substantial proportion of the U.S. population, however, is exposed to very little sunlight, especially during certain seasons, so a dietary supply is needed.  Excessive intake of vitamin D can be toxic.)

However, some of the same studies document a higher intake in vegetables, legumes, and fiber and a lower intake of refined sugars, saturated fat, and cholesterol. Upon extensive review of the effects of vegetarian diets in various medical conditions, researchers concluded that 'dietary intervention with a vegetarian diet seems to be a cheap, physiologic and safe approach for the prevention, and possible management of modern lifestyle diseases.' diseases in which a positive association was make are diabetes, cardiovascular disease, stroke, dementia, age-related macular degeneration, gastrointestinal disease, and cancer. The preventive mechanism at work in the vegetarian diet is the rich supply of monounsaturated and polyunsaturated fatty acids, fiber, complex carbohydrates, antioxidants, and a restriction in saturated fat. To reap the benefits of a vegetarian diet, a well-balanced diet from a variety of foods is necessary. The American Dietic Association and the Dietitians of Canada state that 'well-planned vegan, lacto-vegetarian, and lacto-ovo-vegetarian diets are appropriate for all stages of the life cycle, including pregnancy and lactation.”

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